The present invention relates to:
refractory composite materials protected against oxidation at high temperature; PA1 precursors or intermediate substances for preparing said materials; and PA1 preparing said materials (by preparing said precursors), and preparing said precursors. PA1 a first step of preparing a slip (precursor of the matrix in the final product): suitable inorganic powders (Si.sub.3 N.sub.4, SiC, . . . ) and appropriate additives (densification additives such as Al.sub.2 O.sub.3 and Y.sub.2 O.sub.3, dispersants, and/or wetting agents, . . . ) are put into suspension in water; PA1 a second step of incorporating fibers (reinforcing fibers) in said slip and of consolidating the whole (shaping by filtering under pressure): at the end of this step, the objective is to obtain a raw product of a density that is as high as possible; and PA1 a third step of densification: this comprises sintering the raw product, which may be performed at a temperature higher than 1600.degree. C., under load (a mechanical pressure is generated, e.g. 27 MPa), in an inert atmosphere or under inert gas pressure (the pressure imposed generally lies in the range 10 bars to 100 bars); in one or other of said contexts the inert gas used generally consists in nitrogen or argon; argon being recommended for use with silicon carbide.
More precisely, the present invention relates to providing protection at high temperature (up to 1500.degree. C. to 1600.degree. C.) in an oxidizing atmosphere for highly refractory ceramic matrix composite materials that are reinforced by fibers that are known for being sensitive to oxygen at low temperature (below 900.degree. C.); said composite materials being made via a solid process.
A solid process is a third process, distinct from the liquid process or the gas process, suitable for making composite materials. It is familiar to the person skilled in the art and generally comprises the following three steps:
A variant of that solid process is described in patent application CA-A-2 145 706.